1. Field of the Invention
The present invention relates to a thermal developing apparatus for developing thermally a photosensitive material, the photosensitive material having an electrically conductive, heat-generating layer. More particularly, the present invention pertains to a thermal developing apparatus capable of uniformly heating the photosensitive material when subjected to thermal development.
2. Description of the Related Art
An image recording system which employs a thermally developable photosensitive material (referred to simply as a "photosensitive material", hereinafter) is arranged such that the photosensitive material which has been exposed in an exposing section is transported to a developing section where it is subjected to thermal development, and the developed material is then transported to a subsequent step.
One example of this type of image recording system is disclosed in the specification of Japanese Patent Laid-Open No. 75247/1984. In this system, the exposed photosensitive material is fed to the area between a guide plate and a hot plate and is tightly clamped therebetween for a predetermined period of time so as to be heated for effecting development.
The specification of Japanese Patent Laid-Open No. 1939/1981 discloses a developing means arranged such that an electrically conductive layer is overlaid on a photosensitive material, and electric current is supplied to this layer so as to directly heat the photosensitive material through the layer.
In a thermal developing apparatus for developing a photosensitive material with the above-described electrically conductive material layer (referred to as the "electrically conductive, heat-generating layer", hereinafter), each of the front and rear ends of a sheet of photosensitive material is clamped by a pair of roller groups including an electrode roller, and a voltage is applied between the front and rear ends of the electrically conductive, heat-generating layer through the electrode rollers, thereby developing thermally the photosensitive material.
As the electrically conductive, heat-generating layer heats up and the photosensitive material is thereby heated, a convection is generated in the air surrounding the photosensitive material, so that the heated air rises and separates from the material, and the cold air flows down around it instead. In consequence, the whole surface of the photosensitive material is not uniformly heated, which leads to unevenly developed image.